[PATCH] libatomic: Fix up libat_{,un}lock_n for mingw [PR119796]

[Jakub Jelinek]

Hi!

Here is just a port of the previously posted patch to mingw which
clearly has the same problems.

Untested though, I don't have Windows anywhere around.

2025-04-14  Jakub Jelinek  <ja...@redhat.com>

        PR libstdc++/119796
        * config/mingw/lock.c (libat_lock_n, libat_unlock_n): Start with
        computing how many locks will be needed and take into account
        ((uintptr_t)ptr % WATCH_SIZE).  If some locks from the end of the
        locks array and others from the start of it will be needed, first
        lock the ones from the start followed by ones from the end.

--- libatomic/config/mingw/lock.c.jj    2025-04-08 14:09:40.988589457 +0200
+++ libatomic/config/mingw/lock.c       2025-04-14 15:39:08.244686172 +0200
@@ -87,21 +87,30 @@ libat_lock_n (void *ptr, size_t n)
 {
   uintptr_t h = addr_hash (ptr);
   size_t i = 0;
+  size_t nlocks
+    = (n + ((uintptr_t)ptr % WATCH_SIZE) + WATCH_SIZE - 1) / WATCH_SIZE;
 
   /* Don't lock more than all the locks we have.  */
-  if (n > PAGE_SIZE)
-    n = PAGE_SIZE;
+  if (nlocks > NLOCKS)
+    nlocks = NLOCKS;
 
-  do
+  if (__builtin_expect (h + nlocks > NLOCKS, 0))
+    {
+      size_t j = h + nlocks - NLOCKS;
+      for (; i < j; ++i)
+       {
+         if (!locks[i].mutex)
+           locks[i].mutex = CreateMutex (NULL, FALSE, NULL);
+         WaitForSingleObject (locks[i].mutex, INFINITE);
+       }
+    }
+
+  for (; i < nlocks; ++i)
     {
       if (!locks[h].mutex)
-       locks[h].mutex = CreateMutex  (NULL, FALSE, NULL);
-      WaitForSingleObject (locks[h].mutex, INFINITE);
-      if (++h == NLOCKS)
-       h = 0;
-      i += WATCH_SIZE;
+       locks[h].mutex = CreateMutex (NULL, FALSE, NULL);
+      WaitForSingleObject (locks[h++].mutex, INFINITE);
     }
-  while (i < n);
 }
 
 void
@@ -109,17 +118,22 @@ libat_unlock_n (void *ptr, size_t n)
 {
   uintptr_t h = addr_hash (ptr);
   size_t i = 0;
+  size_t nlocks
+    = (n + ((uintptr_t)ptr % WATCH_SIZE) + WATCH_SIZE - 1) / WATCH_SIZE;
 
-  if (n > PAGE_SIZE)
-    n = PAGE_SIZE;
+  /* Don't lock more than all the locks we have.  */
+  if (nlocks > NLOCKS)
+    nlocks = NLOCKS;
 
-  do
+  if (__builtin_expect (h + nlocks > NLOCKS, 0))
     {
-      if (locks[h].mutex)
-       ReleaseMutex (locks[h].mutex);
-      if (++h == NLOCKS)
-       h = 0;
-      i += WATCH_SIZE;
+      size_t j = h + nlocks - NLOCKS;
+      for (; i < j; ++i)
+       if (locks[i].mutex)
+         ReleaseMutex (locks[i].mutex);
     }
-  while (i < n);
+
+  for (; i < nlocks; ++i, ++h)
+    if (locks[h].mutex)
+      ReleaseMutex (locks[h].mutex);
 }

        Jakub